Simulation video games are a category of video games generally designed to simulate aspects of a real or fictional reality as closely as possible. A “life simulation” is a sub category of simulation video games in which a player can control one or more virtual life forms (e.g., a simulated human character, an animal, etc.). The SIMS 3™, published by Electronic Arts Inc. of Redwood City, Calif., is an example of a life simulation video game. In The SIMS 3™, a player can create a character for a life simulation and configure its appearance by changing its body type, physical attributes, clothing, or accessories. A player may select from a predefined list of “parts” or “graphical assets” such as hair, hats, pants, shirts, boots, shoes, etc. The player can then assign one or more graphical assets to physical locations on the simulated character. If a player changes the physical appearance of the character by deforming different areas (e.g., making the hips wider, the shoulders broader, the body more muscular, etc.), any graphical asset that has been selected and assigned to that area of the character can be also be deformed accordingly. For example, if a user selects a tight fitting shirt for the character, then decides to broaden the shoulders, the shirt can be changed to conform to the changes to the shoulders of the character. Similarly, if a pair of pants is selected for a character, and the user widens the character's hips, the pants can be changed to conform to the wider hips.
To manage changes in shapes of graphical assets when simulated characters are modified, information should be maintained to control the parameters by which individual graphical assets may be modified. In particular, the maximum amount of deformation (the “delta”) that may be applied to any particular graphical asset needs to be maintained (e.g., to control how far the hips may be widened, etc.) In The SIMS 3™, “blend shapes” are used to maintain the location of the vertices in the mesh of a graphical asset for both neutral (neutral mesh) and extreme outer limit deformations (delta mesh). The user interface would use the two blend shapes to determine the starting and ending point for any modifications/deformations of the character graphical assets in conformance with any modifications made by the user to the physical appearance of the character.
To manage changes in the texture of the surface of a simulated character, “displacement mapping” may also be used. This technique can use a texture or height map to cause an effect where the coordinate position of different points over a textured surface are displaced according to associated values stored in the map (e.g., occlusion, shadowing, silhouettes, etc.). For example, a displacement map may be used to apply wrinkles to a garment, or razor stubble to the face of a character. In some implementations, displacement mapping information may be saved in the form of an image.